BIOMARKERS IN WEAKLY DEVELOPED PALEOSOL (L1 SS1) IN THE LUOCHUAN LOESS SECTION AND RECONSTRUCTED PALEOVEGETATION-ENVIRONMENT DURING THE INTERSTADE OF THE LAST GLACIATION
洛川黄土剖面末次冰期间冰段弱古土壤 (L1 SS1)分子化石及其古植被与古环境*

Using GC-MS,biomarkers from the weakly developed paleosol(L_1SS_(1)) and loess layers(L_(1)LL_(1) and L_(1)LL_(2)) in the Luochuan loess section were measured continuously.All samples are rich in n-alkanes and other biomarkers.The indices,such as W_(g/v)=nC_(31)/(nC_(27) nC_(29) nC_(31)),W_(w/v)=(nC_(27) nC_(29))/(nC_(27) nC_(29) nC_(31)),and(W_(w/g)=)(nC_(27) nC_(29))/nC_(31) not only record the ratios between grass and total vegetation,trees and total vegetation,and trees and grass,but also indicate the vegetation change history.The CPI of all the tested paleosol(L_1SS_1) samples change between 5.60 and 11.50,and much larger than 1,which indicate that the influences unrelated to the climate during the soil formation are neglectable.Based on relative relationship analyses between magnetic susceptibility,grain size,and biomarker indices,it proved that magnetic susceptibility and grain size generally,the relativity reaches as high as-0.81,recorded environmental change and climatic events,while biomarkers are related to paleovegetation changes.Results indicate that vegetation change is more sensitive to the improvement rather than deterioration of the climate,i.e.,when the climate changes from cold-dry to warm-humid,vegetation changes quickly;but when the climate changes from warm-humid to cold-dry,the vegetation change is in a relatively slow pattern.This phenomenon might be attributed to the stability of the vegetation system itself.Biomarkers of all samples analyzed are characterized by a high carbon number majority of C_(31),indicating that grass predominated the vegetation during the interstade of the Last Glaciation in Luochuan area and there was no forest developed during that period.